Internal combustion engines are controlled to maintain a desired air to fuel ratio in the combustion chamber to reduce emissions. Fuel is delivered via electronically controlled fuel injectors, modernly located in intake parts of the engine's cylinders, for example. However, not all injected fuel enters the combustion chamber. Rather, some fuel is stored in the intake manifold of the engine. This phenomenon is known as “wall wetting” and various approaches are available for taking into account the fuel puddles in the intake manifold in controlling engine air fuel ratio.
Individual cylinder compensation can also be used to develop an individual cylinder wall wetting approach. See, U.S. Pat. No. 6,571,771.
The inventors herein have recognized a disadvantage with such approaches. Specifically, although the compensation is performed on an individual cylinder basis, if used for cylinders with deactivated cylinder valves, or cylinders operating in a variety of number of strokes, errors can occur. Specifically, even though cylinder valves may be deactivated, fuel vapors can still leave the fuel puddles and migrate to other cylinders, thereby affecting the inducted air-fuel ratio. As such, depending on the operating mode of the engine, different physical phenomena may occur.